mesos-slave: --help output for "--master" is incomplete

  --master=VALUE                                May be one of:
                                                  zk://host1:port1,host2:port2,.../path
                                                  zk://username:password@host1:port1,host2:port2,.../path
                                                  file:///path/to/file (where file contains one of the above)

  --master=VALUE                                May be one of:
                                                  host:port
                                                  zk://host1:port1,host2:port2,.../path
                                                  zk://username:password@host1:port1,host2:port2,.../path
                                                  file:///path/to/file (where file contains one of the above)